This movement represents an early, short-lived experiment: the newly invented balance spring. Tompion omitted a fusee—a cone-shaped device used to even out the force in the timekeeping mechanism as the spring unwinds. His fine workmanship, the ingeniousness of his designs, and the greatly improved accuracy of his timepieces contributed vastly to the fame of English clockmaking in his lifetime. Nathaniel Delander was one of Tompion’s favored casemakers.
Signature: Signed on back plate of movement: Tho. Tompion London
Marking:  Crab, struck twice on head of pendant (mark of French provinces in use 1838 to present, for silver, restricted warranty);  ND conjoined (on the interior of the case, for Nathanial Delander)
Frederick George Hilton Price , London (in 1898–before 1912; to Morgan) ; J. Pierpont Morgan , London and New York (by 1912–17; to MMA)
Artist: Watchmaker: Thomas Tompion (British, 1639–1713)Date: 1685–86Medium: Outer case: red tortoiseshell with silver inlay; Inner case and champlevé dial: silverAccession: 17.190.1487a, bOn view in:Gallery 517